1. Field of the Invention
This invention relates to a method for manufacturing dipeptides and more particularly to a method in which an N-substituted aspartic acid and a lower alkyl ester of phenylalanine are subjected to reaction carried out in an organic solvent using an immobilized enzyme to produce a dipeptide.
2. Description of the Prior Art
Enzymes are proteinous compounds which function to catalyze vital reactions to an extremely great degree. Generally, however, the enzymes are not only expensive but also unstable and thus have been utilized in a very narrowly limited range of reactions for industrial purposes. In view of the excellent catalytic function of the enzymes, researches for their industrial applications have recently been actively conducted. As a result of such researches, it has become possible to improve the enzyme stability by immobilizing them. Further, their repeated use and continuous processes for the reaction also have become possible to permit their utilization for industrial purposes. However, in an organic solvent, the activity of the enzymes are very low. Besides, they easily become denatured and deactivated in the organic solvent. Hence, the use of the enzymes have been restricted to an aqueous medium. Thus there has been great restriction also in that respect.
In relation to an enzymatic reaction in an organic solvent, it is known to obtain acetyl-L-tryptophan ethyl ester from acetyl-L-tryptophan and ethyl alcohol.
Further, it has long been known that a proteolytic enzyme serves to catalyze a peptide linkage forming reaction in an aqueous medium. However, there has been no report on such a reaction in an organic solvent. Meanwhile the present inventors have previously proposed a method in which an N-substituted monoaminodicarboxylic acid is reacted with an aminocarboxylic acid ester in an aqueous solvent in the presence of a proteolytic enzyme; then the thus resulting dipeptide ester and the aminocarboxylic acid ester are allowed to form an addition compound; and the addition compound is separated. This method is disclosed in Japanese unexamined patent application publication No. 92729/1978.
The present inventors conducted further studies for such reactions and discovered that a peptide linakge forming reaction could be efficiently carried out by allowing an N-substituted aspartic acid and a phenylalanine lower alkyl ester to react in an organic solvent immiscible with water in the presence of an immobilized metallo-proteinase containing water. The present invention is derived from this discovery.